Some views of the tower combination four-color register
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In recent years, the development of newspapers has been a thousand miles. From the past, there were only one thin sheet of paper and two sheets of thick paper. From the past, only black and red pages have been basically colored. With the popularity of color layout in newspaper printing, the original printing equipment of various newspaper printing factories is basically rigid and fixed in the printing method because of the two-layer BB combination structure, semi-satellite structure or all-satellite structure. The position of the layout on the printing device is black, only black can be printed, color can only be printed, and can not be adjusted according to the needs of the layout. In order to adapt to this rapid development, in recent years, the printing equipment newly added by various newspaper printing factories are mostly tower B-B combined structures. The tower BB combination structure has the advantages of flexible printing color sequence combination, good maneuverability, high machine utilization, etc. It can print double-sided full-color sheets, and the color position is not affected by the equipment capability, but because of the printing equipment structure. The characteristics of the above (commonly known as four-color printing) have higher requirements on the printing registration process. The tower type four-layer B-B combination printing group has the same technical performance, and is accurately placed in the machine installation. The gap between the plate cylinder of the B-B printing group and the blanket cylinder and the blanket cylinder and the blanket cylinder is adjusted accurately and the dimensions are the same. The original specifications of the blanket and the pad are the same, and the blanket is installed with the same torque. From the completion of the above parameters, normal printing should be no problem, but in actual printing production, there will be some unstable operation of the tape between the BB printing groups, and the tension is not enough. Swing, irregular twisting, wrinkling, etc. affect the printing registration.
In the following, some problems appearing in the production of the tower type B-B combined structure printing group are discussed. The phenomenon and solution of the overprinting error caused by the unstable operation of the paper strip in the rotary printing are discussed.
The web paper tape enters the first color roller of the printing group after the paper feeding section passes the tension floating roller. Since the paper roll has a tension control device to bring appropriate tension to the paper, the paper tape is moderately tensioned at this position. And smooth. After the first color printing cylinder is embossed, the paper strip enters the second color printing cylinder through a short distance. The tape is not prone to any large change in the distance between the paper feeding portion and the second color roller, and the registration of the first and second colors is basically in accordance with the standard. After the paper tape is adsorbed by the dampening water and ink of the two plates of the two sets of drums, the physical properties of the tape itself have begun to change, and there is no compactness when it is just pulled out from the paper roll. The paper body became soft and became sticky due to the adhesion of ink to the surface of the tape. Therefore, the distance from the second color printing cylinder to the third color printing cylinder or from the third color printing cylinder to the fourth color printing cylinder is prone to unstable paper running, insufficient tension, and paper swaying. In other cases, the overprinting is not allowed or moved; in severe cases, irregular twisting and wrinkling may occur, and the last two colors cannot be printed at all.
For this type of situation, in order for the printing to be completed smoothly, it is necessary to solve the problem of how to maintain sufficient tension between the four-layer B-B printing group. When the tape passes through the first two sets of printing cylinders, the tension is substantially obtained from the roll tension control system. However, after the paper strip enters the two sets of printing cylinders, the paper roll tension control system cannot provide sufficient tension to the paper strip because the paper strip is affected by the embossing pressure of the first two sets of printing cylinders. At this time, it is necessary to consider the surface speed of the blanket cylinder of the four-layer printing group. The surface speed of the blanket cylinder of the four-layer printing group should be substantially the same or that the surface speed of the rubber cylinder of the third and fourth printing groups is slightly larger than the first and second. The surface speed of the blanket cylinder of the layer printing group is such that the tape can be properly tensioned throughout the printing process to maintain the smoothness of the tape.
Based on the above considerations, the solution to the problem can be found from the deformation characteristics of the blanket, the rolling principle of the blanket cylinder, and the center distance of the blanket cylinder.
Each of the printing cylinders of the rotary press is relatively rolling under mutual pressure. Although the rotary printing presses used in the present are basically all air-cushion blankets, the embossing of the rubber sheets on the adjacent sides of the rubber sheet is theoretically no more convex bulging phenomenon due to the elastic effect of the air cushion layer. However, in the actual use of the rotary printing press, the elastic ability of the blankets of the two blanket cylinders to return to the original state immediately after the relative rolling pressure is tens of thousands of times per hour and the compression deformation of the plate cylinder and the other blanket cylinder, The elastic ability of the blanket to quickly restore the original shape is caused by the compression of the rubber unit body in the blanket into the embossing area, and the pressure of the rubber unit body disappears away from the embossing area. Since rubber has the property of delaying high elasticity, the development of high elastic deformation always lags behind stress. When the last deformation of the rubber unit body has not yet disappeared due to the rebound, the next stress is applied again, so that the rubber is continuously circulated, and the elastic energy stored inside the rubber is not released, and is converted into heat to be released. The more heat is released, the greater the internal friction of the rubber. The higher the stress frequency of the blanket, the less the elasticity of the blanket will be, so that the air cushion blanket will be slightly similar on the adjacent sides of the rubber sheet laminate line. Hysteresis of convex convex deformation. Therefore, when the two blanket cylinders are rolled, the circumferential length of the blanket actually rotated by the effect of the diameter increasing effect is greater than the circumferential length of the blanket when the pressure is not pressed. Moreover, the greater the pressure, the higher the convex hull is produced, and the longer the circumference of the blanket is rotated. This theory is a theory derived from the experiments of the Englishman Miller and is the result of an increase in diameter effect.
Combining this theory with the working mode of the rotary press rubber cylinder, the two blanket cylinders are regarded as interacting impression cylinders. After the rubber cylinder is pressed, the rolling radius will increase and the rolling radius of the blanket cylinder will increase. The ratio to the free radius is the rolling ratio. The rolling ratio directly affects the walking speed of the paper, which is very helpful for whether the paper is moderately tensioned and the marking is clear and accurate.
The factors that affect the rolling ratio are as follows:
1. The characteristics of the blanket, different types and different characteristics of the blanket have different rolling ratio. The blanket is mainly selected from the following characteristics:
(1) Hardness: The ability of rubber to resist the intrusion of other substances into its surface. It is necessary to take into account the quality of the printed matter, the printing durability of the printing plate, the manufacturing precision of the printing press, and the flatness of the blanket itself.
(2) Elasticity: The ability of the blanket to return to its original state immediately after removing the external force that causes it to deform. During the printing process, the blanket is deformed by the pressure of another blanket cylinder. When the pressure is turned away from the surface of the blanket cylinder, the blanket is required to quickly return to the original state to receive the ink on the printing plate. Then, it is quickly restored to the original state, and the carried ink is transferred to the paper by pressure with another blanket cylinder.
(3) Compression deformation: the strength of rubber deformation after repeated compression of the blanket. When the blanket is printed, it undergoes numerous compression recovery processes, which cause compression fatigue and permanent deformation. At this time, the thickness of the blanket will be reduced and the elasticity will be reduced.
2. Compression of the blanket: The same blanket has different rolling ratios at different compressions. When the two blanket cylinders are rolled, the circumference of the blanket actually rotated is greater than the circumference of the blanket when it is not pressed. The greater the pressure, the longer the circumference of the blanket. This shows that by changing the center distance between the blanket cylinder and the blanket cylinder, different roll ratios can be obtained, and the surface speed of the blanket cylinder can be changed. In the actual use adjustment, the center distance between the rollers can be different as long as there is a difference of about 0.01 mm to 0.02 mm.
3. The tightness of the blanket: the amount of the blanket beyond the original length under a certain tension. The elongation of the blanket is generally expressed by the elongation. The smaller the elongation of the blanket, the better, the elongation is large, and the rubber is easy. When stretched, the rubber layer will be thinned and the elasticity will be reduced. The tighter the blanket is, the thinner it is. The smaller the free radius of the blanket cylinder, the larger the rolling ratio will be, because the rolling ratio will increase and the rolling radius of the blanket cylinder will be larger. The blanket must be taut on the blanket cylinder under the appropriate tension. If the blanket is too loose, when the blanket is imprinted, it will be displaced under the action of the pressing force and cannot be reset in time, which may cause malfunctions such as ghosting. The blanket is stretched too tightly, and the blanket layer is thinned and the elasticity is lowered. Especially the air cushion blanket which is basically used on the rotary printing machine. If the tension is too tight, the microbubble sponge layer may be invalidated, and the air cushion blanket should be lost. With good performance, the synchronous rolling ratio of the blanket cylinder relative to the plate cylinder and the impression cylinder will rise, which will destroy the synchronous rolling state.
From the inspection in actual production, the above adjustments have a good effect on improving paper running. A problem with the tape running from the second color printing cylinder into the third color printing cylinder or from the third color printing cylinder into the fourth color printing cylinder can basically find a solution from the above theory.
1. In the case that the mechanical parameters of the machine and equipment are not changed, a rubber with a higher hardness can generate sufficient printing pressure with a small amount of deformation. At this time, the thickness of the blanket pad is reduced, the free radius is reduced, and the synchronous roll ratio is increased; on the contrary, the blanket having a lower hardness needs to increase the thickness of the blanket pad when the same printing pressure is reached. The free radius of the drum is increased and the amount of compression is increased. At this time, the synchronous rolling ratio becomes smaller, which causes deformation of the dot and affects the registration effect. Therefore, by using the same size blanket with a hardness higher than that of the first three color printing cylinders in the fourth color printing cylinder, the paper can be moderately tensioned.
2. In the case where the specifications and dimensions of the four-color printing cylinder blanket and the liner are uniform, the center distance of the two blanket cylinders in the third and fourth color printing cylinders is changed, so that the compression amount of the blanket complies with the theory of the diameter increasing effect. The change achieves the effect of increasing the surface speed of the third and four-color printing cylinders. However, if the compression amount of the blanket is simply changed in a state in which the size of the blanket and the pad are uniform, the deformation of the four-color dot may affect the registration. At this time, it is necessary to balance the relationship between the center distance adjustment of the roller, the adjustment of the pad size, the operation of the tape and the printing registration, and the technical properties of the printing material such as the hardness of the blanket, the hardness of the pad and the weight of the paper. Have a close relationship. In actual production, try to reduce the center distance of the roller, and reduce the original size of the gasket to obtain the desired effect.